The invention relates generally to electronic display technology and more specifically to volumetric three-dimensional displays.
It is known that it is possible to create a three-dimensional image by illuminating a rotating two-dimensional surface. A series of points or trajectories (i.e., vectors) is displayed by controlling the time-varying illumination of a projection surface. As the projection surface sweeps out a 3-D volume, many points in the 3-D volume can be illuminated. Due to the persistence of human vision, if a point is repeatedly illuminated for a brief interval with a repetition period of no more than {fraction (1/20)} second, the point appears to be illuminated without flickering. Thus, by illuminating a display screen which undergoes rapid periodic motion to sweep out a volume of space, a true volume-filling (i.e., volumetric) 3-D display can be achieved.
One such system is described by Ketchpel (U.S. Pat. No. 3,140,415). His system utilizes a phosphorescent rotating screen that is illuminated by a fixed electron gun. His approach, however, is characterized by xe2x80x9cdead zonexe2x80x9d regions which are not addressable or accessible by the illumination source. For example, when the angle between the screen""s plane and the impinging illumination beam is small, it is difficult to draw imagery of high detail. In such regions, the imaging volume has picture elements (i.e., voxels) that are plagued with low spatial accuracy.
Schwarz and Blundell attempted to solve this problem by using a similar phosphorescent screen system and illuminating it with two electron guns, each responsible for illuminating the screen during different angular segments (IEEE Proc.xe2x80x94Optoelectron., Vol. 141, No. 5, October 1994, pp. 336-344). This helps eliminate the dead zone but requires duplicate illumination, computation, and aiming systems and circuitry.
In contrast, Batchko (U.S. Pat. No. 5,148,310) employs a single illumination source, which shines onto a rapidly moving scanning system. In his system, the scanning system is positioned to always illuminate the rotating screen from a direction nearly perpendicular to the screen. His approach, which requires the spinning of a set of mirrors at least one of which is an off-axis mirror, helps reduce the scanning dead zone. Also, his system, like the systems of Ketchpel, Schwarz and Blundell, and many others, is a vector-based scanning system which employs a computationally intensive technology that is known to flicker when drawing complex imagery.
Tsao et al. (U.S. Pat. No. 5,754,147) disclose a volumetric display which, like the Batchko technology, attaches an off-axis mirror to the rotating display unit. They describe a display that is made of three subunits, namely, an optical data generator, an optical interfacing unit, and a rotating unit with display means. Their optical data unit includes an image projector whose generated images are projected into a complex of coaxially rotating mirrors. The mirrors rotate at a different speed than the rotating display screen. They relay light to another mirror, which rotates off-axis with the display screen at approximately 10 Hz. Their optical interfacing unit includes 5 to 10 miniature mirrors.
Garcia Jr., et al (U.S. Pat. No. 5,042,909) employed a rotating screen illuminated by vector-scanned laser light. As their screen rotates, a system of computer-controlled scanners steers laser light onto it. This technique exhibits some of the same characteristics of vector-based displays. For instance, only a low percentage of the addressable volume may be used in a given image.
Favalora (U.S. Pat. No. 5,936,767, entitled xe2x80x9cMultiplanar Autostereoscopic Imaging System,xe2x80x9d and incorporated herein by reference) discloses a raster-based imaging system that is computationally simpler than the vector scanned systems and uses fewer moving parts than some of the systems described above.
For a 3-D display to remain economically feasible, it is desirable that it not require the use of coherent light (i.e., laser illumination). Laser light is presumably used in most of the above-mentioned 3-D displays because it is easy to focus coherent light onto the rotating image plane. In contrast, the Tsao et al. system allows for the use of incoherent light but at the expense of mechanical complexity and decreased brightness in the resulting image. A method of using inexpensive incoherent illumination is disclosed in Morton""s xe2x80x9cThree dimensional display system,xe2x80x9d (U.S. Pat. No. 4,922,336). Morton also discloses the use of an anamorphic lens which rotates coaxially with a helical projection screen so that the illumination is always focused onto the appropriate locations of the screen. However, Morton also uses as his image generator a xe2x80x9cprojection CRT display.xe2x80x9d Typical projection CRTs are slow (e.g. on the order of 60 Hz refresh).
The above-mentioned volumetric 3-D displays provide imagery with nearly every depth cue, most notably convergence (i.e., the viewer""s eyes rotate inwards as a function of nearness) and accommodation (i.e., the viewer""s lenses focus farther as function of depth). However, all known multiplanar, 3-D displays, including those described above, have been unable to render imagery which exhibits occlusion (i.e., the tendency of objects in the foreground to block those in the background). This is because the illuminated regions are naturally transparent. The resulting imagery possesses a ghost-like transparent quality which prevents the viewer from enjoying the occlusion of objects placed in front of each other.
For only one viewer, occlusion is produced in the displayed image by providing the rendering software with knowledge of the viewer""s position. If the rendering software that computes the image slices that are to be displayed is capable of hidden surface removal, it can render a view appropriate for the viewer""s position. The position information may be input manually or acquired with existing head-tracking or eye-tracking systems. However, for any additional viewer located at another position different from the first viewer""s position, the imagery will appear confusing because the occlusion will be incorrect. Although steps can be taken to lightly render the xe2x80x9chidden surfaces,xe2x80x9d the effect will still be incomplete.
Generally, it is desired that multiple users be able to use the 3-D display simultaneously. It is also desired that the xe2x80x9cviewer trackingxe2x80x9d be done implicitly without active head-tracking equipment, which tends to be slow and expensive. At the same time, the 3-D display must continue to provide cues for convergence and accommodation.
In general, in one aspect, the invention is a display system including a lenticular screen; a support assembly movably supporting the lenticular screen; and a drive mechanism which during operation causes the lenticular screen to repeatedly sweep through a volume of space.
Preferred embodiments may include one or more of the following features. The lenticular screen is helical in shape and includes an array of cylindrically-shaped lens elements or spherically-shaped lens elements, or some combination thereof. The array is an M by N array. The support assembly defines an axis of rotation for the screen. The screen has an axis of symmetry and is mounted in the support assembly with axis of rotation and the axis of symmetry being collinear. The drive mechanism during operation rotates the screen continually about the axis of rotation. The lenticular screen is translucent. The screen is made up of an array of lenticular elements and a sheet of material having a back surface and a front surface, wherein the array of lenticular elements is on only the front surface. The back surface of the sheet of material is smooth.
In general, in another aspect, the invention is a lenticular screen that is translucent and helical in shape.
In general, in yet another aspect, the invention is a volumetric display including ganged SLMs within the image generator. The ganged SLMs are operated sequentially, each one handling a different projected image slice.
Systems embodying the invention exhibit one or more of the following advantages in comparison to prior art systems. They provide a 3-D display which can exhibit the occlusion of imagery using variable transparency, for one viewer and for multiple viewers. They can provide realistic imagery which does not suffer from constant transparency. They are economical and do not require cumbersome reflective scanning means which rotate quickly with respect to the display unit. They do not include a large number of fixed beam-steering optics to ensure that the illumination reaches the final scanning member. They provide a 3-D display with a minimum of moving mechanical elements. They do not use duplicate illumination sources, which require additional computational effort and hardware to support. They do not require coherent illumination, which is can be costly and dangerous. They do not use screen geometries which introduce significant dark regions known as dead zones. They do not require specialized and expensive computational systems. They can provide multicolor imagery without undue cost. In addition, they allow a design flexibility in the which the screen can either be used in a xe2x80x9cprojection screenxe2x80x9d mode, such as a diffusive surface, or a xe2x80x9cnon-projection screenxe2x80x9d mode, such as a mirror which redirects light from an internal imagery source.
Other advantages and features will become apparent from the following description of the preferred embodiments and from the claims.